[Keyframe]

You asked what advantage would it have over rolling rubber, not how would one do it (you wouldn't with current understanding of physics and energy density/portability). Any at advantage vehicle like that is still in the realm of scifi.

[atoav]

Yes but it collides with our understanding of physics as well. Floating anything with significant weight within an air atmosphere requires constant power, you will at least have to profuce an upwards force that is equivalent to the downwards force. Depending on how efficiently that force is transfered you may need much more. A wheel made of rubber or steel (trains are freakingly efficient!) does give you that much cheaper.

Now theoretically one could envision some energy form that is so abundant it doesn't matter anymore that you constantly fight gravity, sure. But what most people seem to imagine is some magical tech that decouples the vehicle from the force of gravity, while still coupling it to the planet (or whatever the next relevant relevant frame of reference is) somehow. This kind of magical tech makes sense in films or scifi books, but if we just collect together what it would need to be, it is hard to envision any actual potential mechanism short of "we live in a Matrix and we lesrn to control the program".